Electric discharge device



Nov. 14, 1944. w} G SHEPHERD 2,362,937

ELECTRIC DISCHARGE DEVICE Filed Sept. 15, 1942 FIG.

FIG. 2

- INVENTOR n. G. SHEPHERD 4 TTORNEV Patented Nov. 1944 William G.Shepherd, Summit, N'..J., assi'gnor to 1 Bell Telephone Laboratories,Incorporated, New I .York, N. Y., a corporation of New York ApplicationSeptember 15, 1942, Serial No.'45s,ss9

' 5 Claims.. (01. 250-275) This. invention relates toselectric dischargeidevices and more particularly to gaseous discharge devices'of-the gridcontrolled type.

.One. object of this invention'is to-decrease the deionization. time ofgaseous discharge. devices, of the grid. controlled type whereby theoperating trequen-cy range thereof is increased. and their efiicacy inpulse generating systems andthe like,v for example in harmonic producersfor carrier supply in telephone systems such as disclosed l2, the innersurface of which is coated with a thermionic material, and a heaterfilament l3 embedded in an insulating, preferably ceramic,

in my Patent. 2,314,739, granted March 23, 1943,

is enhanced.

Another object of this invention is to increase the. operating life ofgaseous discharge devices of thegrid-controlled type.. H I

In one illustrative. embodimentof this invention, a gaseous. dischargedevice comprises a cathode, an. anodeand a control e ectrode or gridhaving an apertured portion between the cathode and the anode.

In accordance withone feature ofthis invention, thev cathode is anopen-ended hollow memher, for example frusto-conical in form, theinnersurface of whichis electron emissive and in axial alignment with theanode, and an auxiliary or deionization electrode is provided adjacentthe end of the cathode furthest from the anode. The

auxiliary or deionization electrode is maintained at a fixed negativepotential with respectto the cathode during operation of the device andserves to decrease the deionization time of the device and also toreduce positive ion bombardment of "the cathode emissive surface andthus to increase the operating life'of the device.

The invention and the above-noted and other features thereof will beunderstood more clearly and fully from the following detaileddescription with reference to the accompanying drawing in which:

Fig. 1 is a perspective view of an electric discharge deviceillustrative of one embodiment of this invention, portions of theenclosing vess'eland of the control electrode and cathode being brokenaway to show the internal structure more clearly;

Fig. 2 is a sectional view of the electrode structure in the deviceillustrated in Fig. 1.

Referring now to the drawing, the electric discharge device thereillustrated comprises an enclosing vessel l0 provided with a stem 1 Iand having an ionizable filling, such, for example, as argon at apressure of the order of 0.25 millimeter of mercury.

Supported from the stem is a cathode structure comprising afrusto-conical metallic member body 14, the cathode structure beingmountedgby the leading-in conductors H) for the heater filament l3' andthe leading-in conductor ['6 for thecathode. The cathode is encompassedby a control electrode or grid having a cylindrical wall I1 coaxial withthe cathode and adisc. end

wall. l8 having therein a central aperture l9 axially aligned with theemissive surface of the cathode and of materially smaller diameter thanthe adjacent end of the cathode. The control electrode or'grid issupported bya plurality of rigid metallic supports 20 embedded'in thestem Mounted opposite the end wall It in axial alignment with thecathode is adished anode'i2l,

which is supported by the leading-in conductor 22 therefor sealed in andextending throughthe end of the vessel Ill.

Adjacent the smaller end of the cathode, coaxial with the cathode andSupported bya rigid leading-in conductor 23embed'ded in the'stem l I isan auxiliaryor deionization electrode 24; which may bea. metallic discof substantially the same diameter as'the smaller end ofv the cathode.

The initiation of the discharge between the cathode and the anode iseffected by the application of asuitable potential to the controlelectrocle or grid ll, l8. Because of the form of the cathode emissivesurface, the electrons emanating therefrom are directed toward theopening l9 and a concentrated electron flow is realized.

Inasmuch as the cathode emissive surface is out of direct line with theanode 2| through the aperture l9, it is shielded to some extent by thedisc I8 from bombardment by positive ions produced in the region betweenthe control electrode or grid and'th'e-anode. The auxiliary ordeionization electrode 24, which is maintained at a negative potentialwith respect to the cathode during operation of the device, attractspositive ions and thus protects the cathode emissive surface frombombardment whereby deterioration or de struction in this surface bybombardment is substantially prevented and the operating life of the 1'device is increased. This protection of the oathode emissive surface bythe auxiliary or deionization electrode is particularly effective whenioni-\ zation is first initiated in the device. During the period of,and immediately following initiation of ionization, the ions acquirelarge energies inasmuch as the voltage across the device is high andtheir bombarding effect upon the cathode begin until the potential ofthe control electrode becomes negative with respect to the cathode andthis condition may not occur until some time interval after the maindischarge has been interrupted so that a relatively long deionizationtime results. The auxiliary or deionizing electrode in devicesconstructed in accordance with this invention provides an additionaldeionizing surface which is negative with respect to the cathode so thatit is effective immediately upon cessation of the main discharge fordeionization purposes whereby the deionization time is reduced. It maybe noted also that the deionization electrode obviates the use of largenegative biases upon the control electrode to realize short deionizingtime. The use of large biases upon the control electrode results inimpingement of positive ions upon this electrode with large energies andthis in turn may result in sputtering of material from the controlelectrode and consequent deterioration of the cathode and emissivesurface.

Although a specific embodiment of the invention has been shown anddescribed, it will be understood that it is but illustrative and thatvarious modifications may be made therein without departing from thescope and spirit of this .invention as defined in the appended claims.-

What is claimed is:

1. An electric discharge device comprising an enclosing vessel having anionizable medium therein, a hollow cathode within said vessel and havingits inner surface electron emissive, an

anode opposite one end of said cathode, a con-;

trol electrode adjacent said cathode, and a deionization electrodeimmediately adjacent a portion of said inner surface remote from saidone end of said cathode.

2. An electric discharge device comprising an enclosing vessel having anionizable medium therein, a hollow cathode within said vessel and havinga flaring inner surface coated with electron emissive material, an anodeopposite the larger ,end of said surface, a control electrode adjacentsaid cathode, and a deionization electrode adjacent the other end ofsaid surface.

, 3. An electric discharge device comprising an enclosing vessel havingan ionizable medium therein, a hollow cathode within said vessel andhaving its inner surface electron emissive, an anode opposite one end ofsaid surface, a control electrode having a portion between said anodeand said one end of said surface provided with an aperture of smallerdiameter than said end of said surface, and a deionization electrodeadjacent a portion of said surface removed from said end.

4. An electric discharge device comprising an enclosing vessel having anionizable medium therein, a cathode within said vessel and having aflaring inner surface coated with electron emissive material, an anodeopposite the larger end of said surface, a control electrode having aportion between said anode and said end and provided with an aperture inalignment with said surface and of smaller diameter than said end, and adeionization electrode adjacent the other end of said surface.

5. A electric discharge device comprising an enclosing vessel having agaseous filling therein, a hollow open-ended thermionic cathode withinsaid vessel, the inner surface of said cathode being 'frusto-conical andcoated with electron emissive material, an anode opposite the larger endof said surface, a control electrode including a cylindrical portionencompassing said cathode and an end portion extending between saidanode and said end of said surface, said end portion having therein anaperture in alignment with said cathode and said anode and of materiallysmaller area than said end of said surface, and a disc-shapeddeionization electrode adjacent the other end of said surface.

WILLIAM G; SHEPHERD.

